1. Field of the Invention
This invention relates to a bobbin mainly for use in dyeing, thermal treatment, etc. of synthetic fiber yarns, and more particularly, to a press bobbin for yarn treatment which is fabricated by blow molding and, when compressed, does not cause biting of yarns into the bobbin, whereby occurrence of uneven yarns is avoided.
2. Related Art Statement
It is prevailing to use bobbins which are axially compressible in dyeing synthetic fiber yarns. Many press bobbins have been proposed, for example, in Japanese U.M. Publication No. 55-54692(1980), Japanese U.M. Publication No. 56-55172(1981), etc.
Heretofore, press bobbins of the foregoing type have been manufactured by injection molding, according to which cylindrical wall of a bobbin can be shaped freely in various forms, wherein in order to permit compression, as described above, wall portions having different contraction abilities are arranged in the axial direction or the axial frame is shaped in various bend forms, e.g. a corrugated or crenellated form by the use of molds having configurations conforming to such forms.
The injection molding technique, however, requires an intricate fabrication of a mold for that purpose. Particularly, it is very disadvantageous in economical aspect that every time when ring frames and longitudinal frames constituting a cylindrical wall of outer periphery of a bobbin are changed in their forms to other variants, different molds conforming to such configurations are fabricated.
It has also been attempted to mold the cylindrical wall of a bobbin by blow molding method instead of injection molding.
The accompanying FIG. 6 illustrates a typical example of a blow-molded press bobbin which is molded and fabricated by cramping a parison formed by extrusion molding between molds of a required configuration, blowing air into the parison to dilate it while causing it to cling tightly to the cavity faces. This bobbin is constructed so that the cylindrical wall (1) of the bobbin constitutes indentations in the axial direction thereof and each outwardly projecting portion (2) is defined with passage holes (3) for liquid flow. However, such bobbin thus constructed flexes, when compressed, in the portions having the passage holes to obstruct them and consequently, uniform passage of liquid is impeded, which is responsible for uneven dyeing.
On the other hand, a major problem with press bobbin when yarn treatment is effected with use of it is that bend portions of the press bobbin when compressed protrude inwardly and inner yarn portions of the yarn package bite into the bobbin being pressed with the result that non-uniform dyeing is caused.
According to conventional injection molding method, since wall thickness of a bobbin can be chosen freely, press bobbins have been manufactured in such a wall thickness that bending or flexing can be effected suitably, but most of them were of a kind that bend portions protrude inwardly. Accordingly, those existing bobbins produced by injection molding were not suitable for the purpose of preventing inner yarn portions of the yarn package from meshing with or biting into them, either.
In order to cope with the circumstances stated above, this invention is designed to provide a press bobbin which is fabricated by blow molding method and shaped so that uniform passage of liquid through it may be ensured and biting of inner yarn layers of a yarn package on the bobbin into it may be avoided.